1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive (hereinafter, also referred to as “piezoelectric body”) element having a porous region, a manufacturing method for a piezoelectric/electrostrictive body, and a liquid jet head using the same. In particular, the present invention relates to a piezoelectric/electrostrictive element which is excellent in durability and can be miniaturized while achieving a higher performance, a manufacturing method therefor, and a liquid jet head which is excellent in durability and can be increased in size while achieving a higher performance.
2. Description of the Related Art
A piezoelectric/electrostrictive element is constituted by using a thin film having characteristics such as piezoelectricity, pyroelectricity, or ferroelectricity, and is used as a piezoelectric element, an ultrasonic application element, an electro-optic element, a pyroelectric element, a ferroelectric element, or the like. Specific examples of the piezoelectric/electrostrictive element include a semiconductor memory device such as a nonvolatile memory, a surface acoustic wave element, a bulk acoustic wave element, an acceleration sensor, a piezoelectric actuator, and a pyroelectric infrared ray sensing element. In addition, on a mobile communication market, the piezoelectric/electrostrictive element can also be used as a surface acoustic wave (SAW) device used for filters for RF and IF, a film bulk acoustic resonator (FBAR), or the like. The piezoelectric element of a thin-film oscillator, the piezoelectric actuator, or the like which is used as a key component of telecommunication devices, a television, and the like includes a piezoelectric body and electrodes provided on upper and lower portions of the piezoelectric body, and converts electric charges applied between the electrodes into mechanical energy.
The piezoelectric/electrostrictive element has been produced such that a thin film, which is obtained by mechanically processing a material made of a single crystal having piezoelectricity, pyroelectricity, or ferroelectricity, or a material made of a polycrystalline sintered body, is bonded to a substrate. In recent years, while there are demands for miniaturization of a device, increase in concentration, reduction in weight, and higher performance, the manufacturing method in which the single crystal material having high performance is mechanically processed has a limitation in obtaining higher density. Accordingly, various methods of manufacturing the piezoelectric/electrostrictive element by forming a film using those single crystal materials on a single crystal substrate to be used as a device have been developed.
In recent years, a liquid jet head utilizing the piezoelectric element has been used in many cases because the liquid jet head can be used for an ink jet printer utilized as an output apparatus for a personal computer and the like, with high printing performance, with simple handling, and at low costs. The liquid jet head using the piezoelectric element is, for example, provided with multiple individual liquid chambers to communicate with a common liquid chamber containing ink, transfers displacement of the piezoelectric elements provided so as to correspond to the individual liquid chambers through a diaphragm, and ejects ink inside thereof from a liquid injection or ejection port as liquid droplets.
In recent years, in the liquid jet head, in addition to the demand for improvement of the printing performance, in particular, the higher resolution and high-speed printing, there is a demand for increase in length and reduction in costs. Accordingly, with a structure of a multi-nozzle head having individual liquid chambers miniaturized, achievement of the higher resolution and high-speed printing has been attempted. In order to miniaturize the individual liquid chambers of the liquid jet head, it is necessary to achieve miniaturization, higher density, and higher performance of the piezoelectric element. In order to achieve increase in length and reduction in costs of the liquid jet head, it is necessary to enlarge an area of a substrate used for manufacturing the liquid jet head.
As the manufacturing method for the piezoelectric element of the liquid jet head or the above-mentioned piezoelectric/electrostrictive element, there is proposed a method of enabling miniaturization thereof by, for example, forming an epitaxial thin film made of a piezoelectric/electrostrictive material to be patterned. As a method of forming the epitaxial thin film, a chemical solution deposition (CSD) method (a Sol-Gel method), a sputtering method, an MBE method, a PLD method, a CVD method, and the like are employed. In the sputtering method and the PLD method, atoms or the like emitted by application of an ion beam, a pulse laser beam, or the like to a target are deposited on a substrate such as a single crystal which is heated up, to thereby obtain a desired crystalline thin film by epitaxial growth. In the CVD method and the MBE method, a gaseous raw material is deposited on a substrate such as a single crystal which is heated up, to thereby obtain a desired thin film having desired crystallinity by epitaxial growth. In the Sol-Gel method, a low-temperature sputtering method, and the like, an amorphous film serving as a precursor of a desired crystal film is formed on a substrate, and is then crystallized by energy from an outside such as burning or application of light, to thereby obtain a thin film.
In order to produce the crystalline thin film as a single crystal having a single orientation with the orientation in the same direction, or with uniformity in an in-plane orientation, it is necessary that the substrate or a lower layer on which the thin film is deposited be made of a single crystal, and atoms constituting the thin film to be deposited have excellent crystal lattice matching.
For example, as a material of a lower layer of a PZT piezoelectric/electrostrictive body in a PZT piezoelectric/electrostrictive element, which has excellent crystal lattice matching with a crystal of atoms of the PZT piezoelectric/electrostrictive body, Japanese Patent Application Laid-Open No. 2000-332569 discloses a buffer layer including ZrO2, a stabilized zirconia thin film, and a rare-earth oxide (YSZ), and Japanese Patent Application Laid-Open No. H06-280023 discloses a buffer layer using an SRO which can also be used as an electrode material.
On the other hand, in order to enlarge the area of the substrate used for forming the piezoelectric/electrostrictive element, for example, a method of using a silicon single crystal substrate with a large area such as a 6-inch wafer has been reviewed. In a case where, on the silicon single crystal substrate, a YSZ buffer layer, a Pt lower electrode, and a lead zirconate titanate (PZT) piezoelectric/electrostrictive body are subsequently stacked, a large stress is applied to an inside of a film or an interface between layers due to mismatching of crystal lattice constants between layers including the substrate. As a result, a dielectric constant, a Curie temperature, a coercive electric field, remanent polarization, and the like are changed, degradation of crystallinity may be caused, which may lead to warp of each layer or the substrate and peeling of each layer. Such strain is liable to be increased along with the improvement of the crystallinity of the oriented film made of PZT, and it is extremely difficult to achieve both enlargement of area and improvement of film performance due to the improvement of the crystallinity, which also affects mass production. Particularly, in the liquid jet head, in a case where a piezoelectric/electrostrictive body having high crystallinity is used, interfaces between layers of the piezoelectric/electrostrictive body, the electrode, the buffer layer, the substrate, and the like are liable to be peeled, which raises problems of stability of liquid jet and durability as a device.